AG Neurosensorik (Animal Navigation)

Animal Navigation from molecules to behaviour and cognition

The long-distance navigational abilities of animals have fascinated humans for centuries and challe­nged scientists for decades. How is a butterfly with a brain weighing less than 0.02 grams able to find its way to a very specific wintering site thousands of kilometers away, even though it has never been there before? And, how does a migratory bird circumnavigate the globe with a precision unobtainable by human navigators before the emergence of GPS satellites? To answer these questions, multi-disciplinary approaches are needed. Our group and its collaborators use mathematical modelling, physics, quantum chemistry, molecular biology, neurobiology, histology, computer simulations and newly developed laboratory equipment in combination with behavioral experiments and analyses of field data to achieve a better understanding of the behavioral and physiological mechanisms of long distance­ navigation in insects and birds. In recent years, our main focus has been on unravelling the mechanisms underlying the magnetic senses in birds:

The magnetic senses of migratory birds: from behaviour to molecules and neuronal mechanisms

Migratory birds can use a magnetic compass to find their way, and, at least in North America, they seem to calibrate this magnetic compass after the sun compass each evening (Science 304, 405-408); but how do they sense the reference direction provided by the geomagnetic field? In recent years, two biophysical mechanisms have become established as the most promising magnetodetection candidates: (1) iron-mineral-based sensors in the upper beak connecting to the brain through the ophthalmic branch of the trigeminal nerve and/or (2) light-dependent radical-pair processes in the eyes converting the magnetic signal into a visual signal, which is then processed in visual brain areas (for a review, see Current Opinion in Neurobiology 15, 406-414.). In the past years, we performed a number of combined experiments involving molecular biology, anatomy, chemical analyses, neurobiology and behaviour which has brought us to the conclusion that birds do not only have one, but two different magnetic senses, and both the original hypotheses seems to be generally correct. We have shown that potentially magnetosensitive molecules called cryptochromes are found in highly active neurons of the retina of night-migratory birds (PNAS 101, 14294-14299) and that these cryptochromes possess a number of key biophysical prerequisites that makes them ideally suited as magnetodetectors (PLoS ONE 2(10): e1106). We have also located a specific forebrain area, named Cluster N, which is the only part of a migratory bird’s forebrain being highly active processing sensory information when birds perform magnetic compass orientation. Furthermore, if Cluster N is deactivated, migratory European Robins can no longer use their magnetic compass, whereas their star compass and sun compass abilities are unaffected (Nature 461, 1274-1277). Bilateral section of the trigeminal nerve had no effect on the birds’ ability to use their magnetic compass (Nature 461, 1274-1277), but does that mean that the iron mineral based putative sensors in the upper beak are not magnetodetectors? Our most recent findings have documented that the ophthalmic branch of the trigeminal nerve does indeed also transmit magnetic information to the brain (PNAS 107, 9394-9399).